In recent air-conditioning units, it is considered to decrease volumetric flow of coolant in a refrigerating cycle to design a reduction of compressor's power as requirement for saving power and fuel efficiency. Thus, in a heat exchanger, it is desired to increase a heat exchanging efficiency so as to gain a heat exchanging ability more than of the prior heat exchanger in a less volumetric flow of coolant. Under thus condition, though coolant distribution in the heat exchanger influences on the heat exchanging efficiency largely, it is difficult to find an effective improvement plan for temperature distribution at the small volumetric flow due to the structure in a prior drawn cup type heat exchanger in which a tank is provided only in one side thereof. Therefore, the heat exchanger is in course of shifting from one side tank type of the heat exchanger to a both tank type heat exchanger which has tanks in both sides thereof these days.
Furthermore, there is a case that it is obliged to provide various incidental equipments around an air conditioning unit. In thus case, because minimization of the air conditioning unit is required, minimization of the heat exchanger is more necessary with this requirement. Accordingly, it becomes more important problem to secure the heat exchanging ability more than in prior heat exchangers with satisfying the requirement for minimization of the heat exchanger.
Though various improvements of the heat exchangers are considered from the above-mentioned point, above all, it is recognized as an effective means to improve a tube structure. About the improvement of the tube structure, it is desired to make an equivalent diameter of a flow path smaller as well as promoting flattening of the tube, and further it is considered as an effective means to provide inner fin in a flat pipe.
In the case of forming this tube, a flat pipe with a specific length is formed in advance and inner fin are inserted into the flat pipe and brazed so far. However, according to this method, there is disadvantage that productivity becomes worse because the inner fin must be inserted into every flat pipe.
Accordingly, this applicant adopts a method for producing tubes by a roll forming in order to resolve the above disadvantage. This is that a material for a flat pipe is rolled up so as to cover the inner fin, a flat pipe A is formed while including the inner fin B in the flat pipe as shown in FIG. 10, and then a tube D with a specific length is formed by inserting a cutting blade C from one side in a width direction thereof to cut the flat pipe A together with the inner fin B.
However, because a shape of a prior tube is determined only in a view point that the included inner fin makes an equivalent diameter of the flow path smaller, as shown in FIG. 10, there is a disadvantage that the inner fin B are deformed extremely and the flow path with small equivalent diameter can not be formed because the inner fin B get out of position in an arrow direction illustrated with a broken line (a width direction of the tube) by the cutting blade C when the cutting blade C inserted from the width direction in the case of forming the inner fin in, for instance, a corrugated shape.
It is considered that this disadvantage is caused by that stiffness to a width directional force of the inner fin itself, stiffness to a binding force by the flat pipe from a thickness direction thereof, and further a contact resistance to a width directional force at a contacting portion between the inner fin and the flat pipe are not secured because a shape of the inner fin is determined only in a view point that the equivalent diameter of the flow path is reduced.
Therefore, in this invention, it is a main object to provide tubes for a heat exchanger which can prevent much deformation of the inner fin to secure a flow path with a small equivalent diameter in the flat pipe in the case of cutting the inner fin included in the flat pipe together with the flat pipe in the width direction.
More concretely, the object of the invention is to provide tubes for a heat exchanger so as to increase the stiffness to the width directional force of the inner fin itself and the stiffness to the binding force by the flat pipe in the thickness direction thereof, and further to enlarge the contact resistance to a width directional force at a contacting portion between the inner fin and the flat pipe.